158 THE MICROSCOPICAL NEWS. 
the integument. Each hook is provided with a lateral process, 
Z ~, by which it articulates with an ossicle of crescentic form, a, 
which is also provided with articulating processes, to which the 
lateral processes of the hooks are applied. ‘This ossicle appears to 
me to be concerned in the movement of the hooks, but in what 
way I have not been able to discover. Between its extremities, 
which are sometimes truncated, sometimes pointed, an apparently 
fibrous band may sometimes be seen. The margin of the disc is 
produced into sixteen processes, each of which carries at its apex 
a hooklet, % 2. Each process, with its hooklet, is individually 
motile, the movement being effected by means of a linear tendin- 
ous appendage, 4, which originates in the central portion of the 
disc, on its dorsal surface, and is inserted into the base of the 
hooklet. The hooklets are provided with two wings, to one of 
which the appendage is attached. Careful focussing of the micro- 
scope reveals a number of fine fibrils, which, in the central portion 
of the disc, are longitudinal, and are probably muscular. Attached 
to its finny host by the caudal disc, the animal may often be seen 
restlessly moving to and fro apparently in search of food. At one 
moment it is elongated to three or four times its ordinary length ; 
at another it is so much contracted as to appear almost spherical. 
Locomotion is effected by means of the cephalic lobes, which pos- 
sess considerable prehensile power, and the caudal disc. The 
body is first elongated considerably, and, the cephalic lobes being 
made to adhere to some fixed point, the caudal disc is brought up 
close behind, the body being thrown into the form ofa loop. I 
am not aware that this parasite has been found upon any fresh- 
water fish except the stickleback in this country, but it was found 
upon the gills of pike, carp, gudgeon, bream, Prussian carp, 
minnow, bleak, loach, and pond loach by one of the Continental 
observers. I have occasionally seen a stickleback make frantic 
efforts to rid itself of its tormentors, though I have known several 
to live for two or three weeks with a number of the worms on their 
fins and tails, without appearing to suffer any inconvenience. 
I will now pass on to the consideration of the internal anatomy 
of the animal. The mouth, Figs. 43 and 44 m, when closed appears 
as a transverse slit, but when open it presents an oval or rounded 
aperture, having a wavy margin. The integument around it is 
radially striated. It opens almost vertically into a thin walled 
pyriform pharyngeal sac, Figs. 43 and 44 fs. This sac gives attach- 
ment to eight finger-like tentacular processes, Fig. 45 ¢ 4, which 
can be protruded through the open mouth, when they resemble an 
eight-rayed star, Fig. 46. The upper portion of the sac is divided 
into eight cell-like segments, Figs. 43 and 45 cs., in the centre of 
which a nuclear body, containing a dark nucleolus may be seen, 
the surrounding contents being finely granular. At the junction 
